This invention relates in general to electrophotography and, in particular, to electrically conductive materials and a method of producing such materials for use in an electrophotographic imaging member.
There is a need in various fields for conductive materials which are humidity insensitive and which can be easily coated. Such materials are especially needed for electrophotographic applications. For example, partially transparent conductive ground planes are extensively used in electrophotographic imaging members. These ground planes typically consist of a metal or metal oxide layer on a non-conductive support. The metal/metal oxide layer must be very thin to allow the transmission of light. To achieve thin layers, the metal/metal oxide layer is applied to the substrate by vacuum deposition, adding a substantial cost burden to the imaging member design.
Solvent coating of a ground plane in an electrophotographic imaging member may be performed. However, the materials which can be solvent coated rely on ionic conduction and are generally humidity sensitive.
Charge transfer complexes containing tetracyanoquinodimethane (TCNQ) salts are highly conductive. A large number of charge transfer salts have been synthesized. In 1981, Polish workers published a "note" (Jeszka et al, Nature, vol. 289, Conductive Polymer: Reticulate Doping with Charge-Transfer Complex, Jan. 29, 1981) on the fabrication of conductive polymer films doped with TCNQ salts. A charge transfer complex loading of 2% provided conductivity through a dendritic crystalline network, which was induced by optimized fabrication procedures. These fabrication procedures include a substrate temperature of over 100.degree. C. as well as use of O-dichlorobenzene solutions heated to 170.degree. C., making film coating a difficult task.
U.S. Pat. No. 4,529,538 to Kim reported the effect of various polymers on the conductivity of N-methylphenazine/TCNQ salt. Filamentary (fibril) structures were noted in some of the binders. Although the solutions were coated at room temperature, the preferred use of dimethyl formamide (DMF) as solvent required controlled vacuum drying to achieve the desired conductive structures. Optimum concentration of charge transfer complex in the binder was 35%.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite imaging member comprises finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
Other composite imaging members have been developed having numerous layers which are highly flexible and exhibit predictable electrical characteristics within narrow operating limits to provide excellent images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. In such a device, the conductive layer is typically a metal layer formed by vacuum deposition.
There continues to be a need for conductive materials for electrophotographic applications.